In search of an anaesthesia alternative for field-based research

Chemically induced anaesthesia is currently the only approved method for anaesthetising fish for sampling and surgical procedures by many organizations, including the Canadian Council on Animal Care, Health Canada, and the U.S. Food and Drug Administration (FDA). Although MS-222 (Tricaine-S) performs well, the long chemical withdrawal time makes it a poor choice for field-based research where fish cannot be held very long, especially in areas where commercial, subsistence or recreational fisheries occur. The lack of approved anaesthetic options for field research is mainly due to a lack of research on the suitability of alternatives, particularly for surgery. In the present study, juvenile brook trout (Salvelinus fontinalis) were subjected to a handling stressor or surgical stressor (tag implantation) using one of three anaesthetics: MS-222, AQUI-S (R), and electro-immobilization. Indicators of stress (blood glucose and plasma cortisol) were measured over five time points (0 h, 1 h, 4 h, 24 h, 1 week post-stressor). The results from this study suggest some time-specific differences in stress levels between anaesthetics; however, there was limited evidence to suggest differences in the efficacy of the anaesthetic methods at mediating stress levels in brook trout. Thus, both AQUI-S (R) and electro-immobilization may provide suitable alternatives to MS-222 for field research.